24 - blood vessels and blood pressure Flashcards
(24 cards)
explain arteries
- transports blood leaving the heart
- thick walls
- high pressure
explain capillaries
- thinnest vessel walls
- permit exchange of gases and waste between blood and interstitial tissues
explain veins
- transports blood back to the heart
- thinner walls
- low pressures
- valved to prevent back flow of blood
explain elastic arteries?
- large diameters up to 2.5 cm to carry large volumes of blood
- their elasticity means they can cope with large pressure changes by expanding and contracting
- major blood vessels including the aorta and pulmonary artery.
explain muscular arteries
- smaller in diameter (0.4 cm average) and have a thick tunica media
- contain more smooth muscle cells than elastic arteries
- majority of arteries are muscular
explain arterioles
- smallest intermal diameters
- tunica media consists of scattered smooth muscle cells
- change diameter to control blood flow
explain large veins
large diameters, larger that their artery counterparts.
include superior and inferior vena cava.
explain medium sizes veins
smaller in diameter, comparable to muscular arteries.
tunica media is thin with few smooth muscle cells.
explain venules
smallest internal diameters.
tunica media is lacking in the smallest venules.
some veils contain valves to prevent blood flowing back to the capillaries.
blood from the lower body needs to return to the heart agains gravity.
skeletal muscles contract to help drive the blood back to the heart.
what are capillary beds?
- network of capillaries
- arteriole transfers blood to the venule through this network.
- precapillary sphincters consist of smooth muscle cells which control vessel diameter to control blood flow through the capillaries.
what are capillaries?
capillaries are thin to allow diffusion of gases, nutrients and waste between the lumen (central space that contains blood) of the capillaries and the surrounding interstitial fluid.
explain continuous capillaries
- most common type
- endothelium is the complete lining - connected endothelial cells with tight junctions.
- basement membrane is complete
- permit diffusion of water and lipid-soluble materials into the interstitial fluid.
- prevents blood cell and plasma protein loss.
explain fenestrated capillaries
include pores to allow rapid exchange of water and solutes between blood and. interstitial fluid.
basement membrane is complete so pores are covered.
explain sinusoidal capillaries
most permeable
presence of large intracellular clefts.
allows movement of larger molecules.
basement membrane is incomplete, so pares are open.
how is capillary blood flow determines through pressure and resistance?
FLOW IS HIGH IF:
- the resistance from the capillaries is low
- the pressure difference between the two ends of the vessel is high
FLOW IS LOW IF:
- the resistance from the capillaries is high
- the pressure difference between the two ends of the vessel is low.
so we can say flow is directly proportional to change in pressure.
explain cardiovascular pressure
pressure is needed to push blood through the capillary beds.
blood pressure is highest in the aorta at about 120 mmHg (mm of mercury).
as blood passes through the arteries decreasing in size, the pressure drops until it reaches the capillaries at about 35 mmHg.
blood pressure continues to drop as it flows through the venous system and is lowest in the vena cava.
the mean atrial pressure (MAP) is approximately 100 mmHg.
explain vascular resistance
resistance from blood vessels decreases blood flow.
Resistance is mainly caused by friction between the blood vessels.
Friction is increased due to:
- Increased vessel length
- Decreased vessel diameter
Diameter can be controlled through:
- Vasoconstriction (decreased diameter)
- Vasodilation (increased diameter)
Resistance can also be increased by:
- Increased viscosity of blood
- High turbulence (swirling motion) of blood
Resistance of entire cardiovascular system is called the total peripheral resistance (TPR).
what is vascular compliance?
Compliance is the ability of the blood vessel to expand with blood volume.
- Elastic arteries are more compliant than other arteries
- veins are more compliant than arteries
when is compliance high?
Compliance is HIGH if:
- Change in blood volume is high
- Pressure difference is low
- i.e. in a venule
when is compliance low?
Compliance is LOW if:
- Change in blood volume is low
- Pressure difference is high
- i.e. in an arteriole
where is pressure the greatest?
Pressure is greatest in the aorta and continues to drop as it reaches the vena cava.
where is velocity the highest?
Velocity is greatest in the aorta, drops in the capillaries and increases again in the venous system because resistance in the veins is low.
what is systolic pressure?
Systolic pressure - peak pressure during ventricular systole.
what is diastolic pressure?
Diastolic pressure - lowest pressure during ventricular diastole.
